Method of selecting ions in an ion storage device

Abstract

The present invention describes a method of selecting ions in an ion storage device with high resolution in a short time period while suppressing amplitude of ion oscillation immediately after the selection. In a method of selecting ions within a specific range of mass-to-charge ratio by applying an ion-selecting electric field in an ion storage space of an ion storage device, the method according to the present invention is characterized in that the ion-selecting electric field is produced from a waveform whose frequency is substantially scanned, and the waveform is made anti-symmetric by multiplying a weight function whose polarity reverses, or by shifting a phase of the waveform by odd multiple of π, at around a secular frequency of the ions to be left in the ion storage space. It is preferable that the frequency of the waveforms is scanned in a direction where the frequency decreases. It is also preferable that the weight function is linearly changed at the boundaries of the scanning range of the frequency.

What is claimed is:  
     
       1. A method of selecting ions within a specific range of mass-to-charge ratio by applying an ion-selecting electric field in an ion storage space of an ion storage device, wherein said ion-selecting electric field is produced from a waveform whose frequency is substantially scanned, and said waveform is made anti-symmetric at around a secular frequency of the ions to be left in the ion storage space. 
     
     
       2. The method of selecting ions according to  claim 1 , wherein said waveform is made anti-symmetric by multiplying a weight function whose polarity reverses at around said secular frequency of the ions to be left in the ion storage space. 
     
     
       3. The method of selecting ions according to  claim 1 , wherein said waveform is made anti-symmetric by shifting a phase of said waveform by odd multiple of π, i.e. by adding (2k+1)π, where k is an arbitrary integer, to a phase of said waveform, at around said secular frequency of the ions to be left in the ion storage space. 
     
     
       4. The method of selecting ions according to  claim 1 , wherein the frequency of said waveform is scanned in a direction where the frequency decreases. 
     
     
       5. The method of selecting ions according to  claim 2 , wherein the frequency of said waveform is scanned in a direction where the frequency decreases. 
     
     
       6. The method of selecting ions according to  claim 3 , wherein the frequency of said waveform is scanned in a direction where the frequency decreases. 
     
     
       7. The method of selecting ions according to  claim 1 , wherein said waveform is multiplied by a weight function which is linearly changed at the boundaries of scanning range of frequency. 
     
     
       8. The method of selecting ions according to  claim 2 , wherein said waveform is multiplied by a weight function which is linearly changed at the boundaries of scanning range of frequency. 
     
     
       9. The method of selecting ions according to  claim 3 , wherein said waveform is multiplied by a weight function which is linearly changed at the boundaries of scanning range of frequency. 
     
     
       10. The method of selecting ions according to  claim 4 , wherein said waveform is multiplied by a weight function which is linearly changed at the boundaries of scanning range of frequency. 
     
     
       11. The method of selecting ions according to  claim 5 , wherein said waveform is multiplied by a weight function which is linearly changed at the boundaries of scanning range of frequency. 
     
     
       12. The method of selecting ions according to  claim 6 , wherein said waveform is multiplied by a weight function which is linearly changed at the boundaries of scanning range of frequency. 
     
     
       13. The method of selecting ions according to  claim 1 , wherein said waveform whose frequency is substantially scanned is composed of plural sinusoidal waves with discrete frequencies, where each frequency component of said waveform having a constant part in its phase term which is written by a quadratic function of its frequency or, in other words, by a quadratic function of a parameter which is linearly related to its frequency. 
     
     
       14. The method of selecting ions according to  claim 2 , wherein said waveform whose frequency is substantially scanned is composed of plural sinusoidal waves with discrete frequencies, where each frequency component of said waveform having a constant part in its phase term which is written by a quadratic function of its frequency or, in other words, by a quadratic function of a parameter which is linearly related to its frequency. 
     
     
       15. The method of selecting ions according to  claim 3 , wherein said waveform whose frequency is substantially scanned is composed of plural sinusoidal waves with discrete frequencies, where each frequency component of said waveform having a constant part in its phase term which is written by a quadratic function of its frequency or, in other words, by a quadratic function of a parameter which is linearly related to its frequency. 
     
     
       16. The method of selecting ions according to  claim 1 , wherein a plurality of said ion-selecting electric fields having different speeds of frequency scanning are used to select the ions with high resolution in a short period of time. 
     
     
       17. The method of selecting ions according to  claim 2 , wherein a plurality of said ion-selecting electric fields having different speeds of frequency scanning are used to select the ions with high resolution in a short period of time. 
     
     
       18. The method of selecting ions according to  claim 3 , wherein a plurality of said ion-selecting electric fields having different speeds of frequency scanning are used to select the ions with high resolution in a short period of time.